Don’t get caught out

How can an uninterruptible power supply system contribute to energy efficiency programmes in educational facilities? Alex Emms examines the options for energy managers

Alex Emms

Operations director for Kohler Uninterruptible Power Ltd

www.kohler-ups.co.uk

s significant energy users

Awith varied estates, most educational facilities will devote considerable effort and innovation to reducing their energy bills and carbon footprint. Many have environmental schemes in place to recognise progress.

Their complex nature means educational institutions depend on a resilient, efficient IT infrastructure to support students and staff both on and off-site, and as well as requiring dependable power for life-safety and access control systems to protect their students, staff and visitors.

With the risk of frequency fluctuations, voltage variations and even blackouts increasing as the UK adopts more renewable sources into its grid, comes the need for a back-up power supply which can manage the demands of the educational establishment and keep things functioning without drama. Therefore, an integrated power protection solution that encompasses an uninterruptible power supply (UPS) and generator system is often used.

Protection from power loss

UPS systems with associated batteries will protect the critical loads from power loss and either keep them running until power is restored, a generator comes online or will provide time to shut protected equipment down safely. Note that even if generators are present, uninterruptible power supplies are necessary to support the critical loads until the generators can reach operating speed and frequency synchronisation.

As the total power provided to critical loads can be significant, and this all passes through a UPS, it is important to question how much of that power is lost as it does so – in other words how efficient the UPS is. Similarly, it is vital to recognise the efficiency of a UPS varies across its load range, with the efficiency sweet spot typically at 50 per cent and, in conventional operation, marked deterioration below 25 per cent of rated load.

For this reason, often the most appropriate and energy efficient UPS type for educational facilities is a “static, continuous online, modular N+1 system”.

Electronics and battery bank

A static UPS uses electronics and a battery bank to protect against power disturbances, as opposed to rotary UPS – these instead use a large rotating mass but are typically more bulky, less efficient and more complex to maintain so have almost entirely been replaced by static UPS in educational applications.

Continuous online systems are better for most educational applications as they provide continuous protection against both voltage and frequency variations, as opposed to “line interactive” systems which cut in after a short delay, something which may result in data corruption or equipment shutting down. However, as these are continuously operating their size and format must be carefully considered.

Critical power systems usually have a level of redundancy, defined as the power to support the load, N, and the amount of extra protection. An “N+N” system will have twice the power needed to protect the load, whereas an “N+1” system has enough power to protect the load plus one

There is considerable variation in the quality of systems and service

Universities and colleges are dependent on a robust IT infrastructure

level of redundancy. In a system built of equally sized modules, this extra level can be just one extra module. For a 200kVA load the total system size for an N+N system would need to be 400kVA, whereas for a modular system built up of 50kVA modules the system could be just 250kVA. Apart from the initial purchase cost for a 250kVA system being less than for a 400kVA system, the running costs for the smaller system would also be lower and a system can be gradually expanded as load grows.

Balancing UPS load

Modular systems also have an additional advantage if they have smart, load dependent operating functionality, such as Kohler’s “XTRA VFI” mode. This functionality balances UPS load across its modules so they operate at their most efficient point. If load falls significantly (e.g. overnight), it concentrates the load on certain modules, keeping an additional one active to cover the “+1” redundancy requirement and then putting the others into standby mode to save energy. These can quickly be turned on again, so protection is not put at risk but the energy saving, especially below 25 per cent of rated load, is very significant.

Fixed in place systems

Due to cost, immobility, reliability and environmental impact most UPS systems use Valve Regulated Lead Acid (VRLA) batteries. Lithium-ion systems are lightweight and compact, so great for mobile applications, but UPS systems remain fixed in place. This means the 3X extra cost is unjustifiable and the existing 98 per cent recycling programme for UK VRLA batteries wins out. Advances in battery management from lithiumion batteries have spread to VRLA systems though, where charge balancing systems can now add 30 per cent to typical VRLA service life.

Given the disruption replacing an inappropriate power protection system can cause, or the consequences of it not meeting the need when called upon, it is also worth highlighting there is considerable variation in the quality levels of systems and service in the market today. Energy efficiency claims should be verified – reviewing particularly if they are “up to” and over what band that applies, as well as if they are for “continuous online” mode or “ECO” mode, which is essentially a line interactive mode that will produce a gap in supply if the mains fails. ■